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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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Serpentine and Surprise 'Glaciers, and it is possible that a number of minor glaciers observed on both sides of the fiord constitute with these a general system."
Toboggan Glacier—The Ice Tongue. Toboggan Glacier, on the eastern side of Harri-man Fiord, nearly opposite Serpentine Glacier, descends the fiord wall from a snowfield of unknown extent, from which, three miles to the south, two smaller ice tongues also project. The valley portion of this cascading glacier is about a mile long and from an eighth to a quarter of a mile wide. Below the lip of its hanging valley it has not as steep an ice cascade as the Cataract Glacier and the cascading glaciers of College Fiord have, although it has a slope averaging 12° to 14°, steepening to 29° to 81° at the end. The glacier is clean, except for a medial moraine of black slate, near the northern border, and two small V-shaped areas of ablation moraine at the terminus.
At the terminus (Fig. 48) is a ledge of black slate 12 to 15 feet high, lying exactly at the northern end of the medial moraine, and the main glacial stream emerges from an ice cave immediately west of this. The glacier partly covered this ledge in 1910, sloping back evenly from its top. West of this ledge is a low slate outcrop beneath the terminus of the glacier. One isolated morainic hum mock, 15 or 20 feet from the glacier, and just west of the stream, still had ice in it and was rapidly slumping. The rest of the ice front seemed to rest upon the edge of the gravels, nowhere underlying them, and causing slumping through melting.
The Outwash Gravels. In 1910, Toboggan Glacier terminated just inside its mountain valley, a little over a quarter of a mile from the fiord (1600.feet), at an elevation of about 112 feet above sea level. Between it and the fiord was a very symmetrical outwash gravel plain, projecting into the fiord for about an eighth of a mile as a delta. Above the surface of this outwash fan, which slopes at the rate of 370 feet to the mile, rise a number of ledges of bare rock, and also several small, barren, gravel hillocks and one tree-covered gravel knob. Some of the gravel mounds are remnants of an older dissected outwash plain, while others may be remnants of older terminal moraine built when, as Grant and Higgins 1 believe, the glacier reached practically to tidewater. One large stream flows over the fan near the middle, and one small one on the extreme southern edge. The main stream has shifted slightly since 1905. There are also older outwash gravels, described in a later section.
Advance and Retreat. Grant, Paige, and Higgins visited Toboggan Glacier in 1905 and 1909, determining an advance of 400 feet and then a retreat of about 650 feet between these dates. They found that "in 1905 the center, or most advanced part of the glacier, was 723 feet, as determined by pacing, distant from the cairn (at a, Fig. 48). Just at the extreme front of the ice at this date was a low rock 'ridge crossing the valley. In 1909 the most advanced part of the glacier was 252 feet farther back than in 1905. However, in 1909 a freshly deposited low moraine in the northern half of the plain in front of the glacier indicates that the ice sometime between 1905 and 1909 had been about 400 feet in advance of its position at the earlier date."
A photograph by Grant and Paige (PL CXXXTT, B) shows that the glacier was much more crevassed in 1905 than, in 1910, and that during its retreat the terminus has narrowed slightly on the southern side. It was still receding in July, 1910, having retreated 75 feet at the point of Grant's measurements. Future measurements of the
i Bull. Amer. Geog. Soc., Vol. XLIII, 1911, legend of Kg. 13, p. 837. 22